Track assembly for an all-terrain vehicle (atv) or other tracked vehicle

ABSTRACT

A track assembly for providing traction to an all-terrain vehicle (ATV) or other tracked vehicle. The track assembly may comprise a wheel device for contacting an inner side of an endless track such that a longitudinal end segment of the endless track turns around the wheel device. The wheel device allows a change in curvature of the longitudinal end segment of the endless track when the longitudinal end segment of the endless track contacts an obstacle on the ground. In some embodiments, the wheel device may comprise a resilient wheel that is elastically deformable. In other embodiments, the wheel device may comprise a wheel carrier carrying a plurality of carried wheels.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation, and claims the benefit under 35U.S.C. 120, of U.S. patent application Ser. No. 12/767,895 filed on Apr.27, 2010 and hereby incorporated by reference herein, and claims thebenefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application61/173,627 filed on Apr. 29, 2009 and hereby incorporated by referenceherein.

FIELD OF THE INVENTION

The invention relates generally to tracked vehicles and, moreparticularly, to track assemblies for providing traction to all-terrainvehicles (ATVs) or other tracked vehicles.

BACKGROUND

Tracked vehicles are often used on soft, low friction and/or unevenground, such as earth, mud, ice and/or snow, because of their endlesstracks which enhance their traction and floatation on the ground.

As they travel on the ground, tracked vehicles can encounter variousobstacles (e.g., rocks, portions of trees, debris, ice blocks, bumps orother abrupt changes in ground level, etc.) depending on theirenvironment. Such obstacles can create shocks in track assemblies of thetracked vehicles. Depending on their intensity, these shocks may affectride quality and/or structural integrity of the track assemblies. Also,while most obstacles encountered by tracked vehicles are normally easilysurmounted, some obstacles may sometimes prove more difficult toovercome. This can negatively impact a tracked vehicle's performance byslowing it down or in some cases bringing it to a standstill.

For example, all-terrain vehicles (ATVs) propelled by track assembliesmay be prone to such problems when encountering obstacles on the ground.For instance, in some situations, an ATV's track assemblies mayencounter large rocks, fallen tree portions, or abrupt changes in groundlevel that induce shocks which can be strongly felt by the ATV's rider.In other situations, an ATV may encounter an obstacle such as a largerock, fallen tree portion or abrupt change in ground level which isdifficult to overcome by one of its track assemblies (e.g., due to atendency of a front region of that track assembly to “dig” or “wedge”itself at the obstacle's base instead of climbing over the obstacle).

Similar problems related to encountering of obstacles on the ground canarise with other types of tracked vehicles.

Accordingly, there is a need for solutions directed to facilitate use ofATVs and other tracked vehicles which are susceptible to encounteringobstacles on the ground.

SUMMARY OF THE INVENTION

According to one broad aspect, the invention provides a track assemblyfor providing traction to an all-terrain vehicle (ATV). The trackassembly comprises: a drive wheel for driving an endless track, theendless track having an inner side for facing the drive wheel and aground-engaging outer side for engaging the ground, the drive wheelbeing rotatable about an axle of the ATV; a plurality of support wheelsfor rolling on the inner side of the endless track along a bottom run ofthe endless track, the support wheels being distributed along alongitudinal direction of the track assembly; and a resilient wheel forcontacting the inner side of the endless track such that a longitudinalend segment of the endless track turns around the resilient wheel, theresilient wheel being elastically deformable.

According to another broad aspect, the invention provides a trackassembly for providing traction to an all-terrain vehicle (ATV). Thetrack assembly comprises: a drive wheel for driving an endless track,the endless track having an inner side for facing the drive wheel and aground-engaging outer side for engaging the ground, the drive wheelbeing rotatable about an axle of the ATV; and a plurality of wheels forcontacting the inner side of the endless track along a bottom run of theendless track, at least one of the wheels being a resilient wheel, theresilient wheel being elastically deformable.

According to another broad aspect, the invention provides a trackassembly for providing traction to an all-terrain vehicle (ATV). Thetrack assembly comprises: a drive wheel for driving an endless track,the endless track having an inner side for facing the drive wheel and aground-engaging outer side for engaging the ground, the drive wheelbeing rotatable about an axle of the ATV; a plurality of support wheelsfor rolling on the inner side of the endless track along a bottom run ofthe endless track, the support wheels being distributed along alongitudinal direction of the track assembly; and a wheel device forcontacting the inner side of the endless track such that a longitudinalend segment of the endless track turns around the wheel device, thewheel device allowing a change in curvature of the longitudinal endsegment of the endless track when the longitudinal end segment of theendless track contacts an obstacle on the ground.

According to another broad aspect, the invention provides a trackassembly for providing traction to an all-terrain vehicle (ATV). Thetrack assembly comprises: a drive wheel for driving an endless track,the endless track having an inner side for facing the drive wheel and aground-engaging outer side for engaging the ground, the drive wheelbeing rotatable about an axle of the ATV; a plurality of support wheelsfor rolling on the inner side of the endless track along a bottom run ofthe endless track, the support wheels being distributed along alongitudinal direction of the track assembly; and a leading idler wheellocated ahead of the support wheels, the leading idler wheel comprisinga tire; and a trailing idler wheel located behind the support wheels,the trailing idler wheel comprising a tire.

According to another broad aspect, the invention provides a trackassembly for providing traction to a tracked vehicle. The track assemblycomprises: a drive wheel for driving an endless track, the endless trackhaving an inner side for facing the drive wheel and a ground-engagingouter side for engaging the ground, the drive wheel being rotatableabout an axle of the tracked vehicle; a plurality of support wheels forrolling on the inner side of the endless track along a bottom run of theendless track, the support wheels being distributed along a longitudinaldirection of the track assembly; and a wheel device for contacting theinner side of the endless track such that a longitudinal end segment ofthe endless track turns around the wheel device, the wheel deviceallowing a change in curvature of the longitudinal end segment of theendless track when the longitudinal end segment of the endless trackcontacts an obstacle on the ground.

These and other aspects of the invention will now become apparent tothose of ordinary skill in the art upon review of the followingdescription of embodiments of the invention in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of embodiments of the invention is providedbelow, by way of example only, with reference to the accompanyingdrawings, in which:

FIG. 1 shows a side view of a tracked vehicle in accordance with anembodiment of the invention;

FIG. 2 shows a top view of the tracked vehicle of FIG. 1;

FIG. 3 shows a perspective view of a track assembly of the trackedvehicle of FIG. 1;

FIG. 4 shows a side view of the track assembly of FIG. 3;

FIG. 5 shows a perspective view of the track assembly of FIG. 3 with atrack removed;

FIG. 6 shows a side view of the track assembly of FIG. 5;

FIG. 7 shows a top view of the track assembly of FIG. 5;

FIG. 8 shows an end view of the track assembly of FIG. 5;

FIG. 9 shows an example of a reaction of the track assembly of FIG. 3when encountering an obstacle on the ground;

FIG. 10 shows a side view of the tracked vehicle in accordance withanother embodiment of the invention;

FIG. 11 shows a top view of the tracked vehicle of FIG. 10;

FIG. 12 shows a perspective view of a track assembly of the trackedvehicle of FIG. 10;

FIG. 13 shows a side view of the track assembly of FIG. 12;

FIG. 14 shows a perspective view of the track assembly of FIG. 12 with atrack removed;

FIG. 15 shows a side view of the track assembly of FIG. 14;

FIG. 16 shows a top view of the track assembly of FIG. 14;

FIG. 17 shows an end view of the track assembly of FIG. 14;

FIGS. 18 and 19 show components of a wheel device of the track assemblyof FIG. 12;

FIG. 20 shows an example of a reaction of the track assembly of FIG. 12when encountering an obstacle having a relatively small size; and

FIG. 21 shows an example of a reaction of the track assembly of FIG. 12when encountering an obstacle having a relatively large size.

It is to be expressly understood that the description and drawings areonly for the purpose of illustrating certain embodiments of theinvention and are an aid for understanding. They are not intended to bea definition of the limits of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 1 and 2 show a tracked vehicle 10 in accordance with an embodimentof the invention. More specifically, in this embodiment, the trackedvehicle 10 is an all-terrain vehicle (ATV), which is a small openvehicle designed to travel off-road on a variety of terrains, includingroadless rugged terrain, for recreational, utility and/or otherpurposes.

In this embodiment, the ATV 10 comprises a prime mover 12, a pluralityof track assemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂, a steering unit 20, and aseat 18, which enable a driver of the ATV to ride the ATV 10 on theground.

The prime mover 12 is a source of motive power that comprises one ormore motors (e.g., an internal combustion engine, an electric motor,etc.). For example, in this embodiment, the prime mover 12 comprises aninternal combustion engine. In other embodiments, the prime mover 12 maycomprise another type of motor (e.g., an electric motor) or acombination of different types of motor (e.g., an internal combustionengine and an electric motor) for generating motive power to move theATV 10.

The prime mover 12 is in a driving relationship with one or more of thetrack assemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂. That is, motive power generatedby the prime mover 12 is transmitted to one or more of the trackassemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂ via a powertrain of the ATV 10.

In this case, the seat 18 is a straddle seat and the ATV 10 is usable bya single person such that the seat 18 accommodates only the driver ofthe ATV 10. In other cases, the seat 18 may be another type of seat,and/or the ATV 10 may usable by two individuals, namely the driver and apassenger, such that the seat 18 may accommodate both the driver and thepassenger (e.g., behind one another or side-by-side) or the ATV 10 maycomprise an additional seat for the passenger.

The steering unit 20 enables the driver of the ATV 10 to steer the ATV10. In this case, the steering unit 20 comprises handlebars. In othercases, the steering unit 20 may comprise a steering wheel or other typeof steering device.

The track assemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂ provide traction to the ATV10 on the ground.

The track assemblies 16 ₁, 16 ₂ are located in a rear part of the ATV 10to provide traction in this rear part. With additional reference toFIGS. 3 to 8, in this embodiment, each track assembly 16 _(i) comprisesa frame 44, a drive wheel 42, a plurality of support wheels 50 ₁-50 ₈, aplurality of wheel devices 54 ₁-54 ₄, and an endless track 41 disposedaround these wheels and wheel devices.

The track assembly 16 _(i) has a first longitudinal end 57 and a secondlongitudinal end 59 that define a length of the track assembly 16 _(i).A width of the track assembly 16 _(i) is defined by a width of theendless track 41. The track assembly 16 _(i) has a longitudinaldirection, transversal directions including a widthwise direction, and aheight direction.

The endless track 41 provides traction to propel the ATV 10 on theground. The track 41 has an inner side 45 facing the wheels 42, 50 ₁-50₈ and the wheel devices 54 ₁-54 ₄ and defining an inner area of thetrack 41 in which these wheels and wheel devices are located. The track41 also has a ground-engaging outer side 47 opposite the inner side 45and engaging the ground on which the ATV 10 travels. In this embodiment,the inner side 45 of the track 41 comprises a plurality of driveprojections (sometimes referred to as “drive lugs”) that are spacedapart along the longitudinal direction of the track assembly 16 _(i) andthat interact with the drive wheel 42 in order to cause the track 41 tobe driven. The ground-engaging outer side 27 comprises a plurality oftraction projections (sometimes referred to as “traction lugs” or“traction profiles”) that are spaced apart along the longitudinaldirection of the track assembly 16 _(i) and engage the ground to enhancetraction.

In this embodiment, the endless track 41 comprises an elastomeric body,i.e., a body comprising elastomeric material, which allows the track 41to elastically change in shape as it is in motion around the wheels 42,50 ₁-50 ₈ and the wheel devices 54 ₁-54 ₄. The elastomeric material canbe any polymeric material with the property of elasticity. In thisembodiment, the elastomeric material includes rubber. Various rubbercompounds may be used and, in some cases, different rubber compounds maybe present in different areas of the track 41. In other embodiments, theelastomeric material may include another elastomer in addition to orinstead of rubber (e.g., polyurethane elastomer). Also, in thisembodiment, the track 41 comprises one or more reinforcements embeddedin the elastomeric material (e.g., a layer of reinforcing longitudinalcables and/or a layer of reinforcing fabric).

The track 41 may be constructed in various other manners in otherembodiments. For example, in some embodiments, the track 41 may comprisea plurality of parts (e.g., rubber and/or metallic sections)interconnected to one another to form an endless belt, the track 41 mayhave recesses or holes that interact with the drive wheel 42 in order tocause the track 41 to be driven, and/or the ground-engaging outer side47 of the track 41 may comprise various patterns of tractionprojections.

The endless track 41 has a top run, which extends between and above thelongitudinal ends 57, 59 of the track assembly 16 _(i), and a bottomrun, which extends between and below the longitudinal ends 57, 59 of thetrack assembly 16 _(i).

The drive wheel 42 is rotatable about an axle 49 of the ATV 10 fordriving the track 41. That is, power generated by the powertrain of theATV 10 can rotate the axle 49, which rotates the drive wheel 42, whichimparts motion of the track 41. In this embodiment, the drive wheel 42comprises a drive sprocket engaging the drive projections of the innerside 45 of the track 41 in order to drive the track 41. In otherembodiments, the drive wheel 42 may be configured in various other ways.For example, in embodiments where the track 41 comprises recesses orholes, the drive wheel 42 may have teeth that enter these recesses orholes in order to drive the track 41. As yet another example, in someembodiments, the drive wheel 42 may frictionally engage the inner side45 of the track 41 in order to frictionally drive the track 41.

The frame 44 supports various components of the track assembly 16 _(i),including the support wheels 50 ₁-50 ₈ and the wheel devices 54 ₁-54 ₄.More particularly, in this embodiment, the frame 44 comprises three (3)frame elements 43 ₁-43 ₃ defining a generally triangular shape. Each ofthe support wheels 50 ₁-50 ₈ and the wheel devices 54 ₁-54 ₄ is mountedto the frame element 43 ₁. Specifically, the wheel devices 54 ₁, 54 ₂are mounted to the frame element 43 ₁ in a front longitudinal end region89 of the track assembly 16 _(i), the wheel devices 54 ₃, 54 ₄ aremounted to the frame element 43 ₁ in a rear longitudinal end region 99of the track assembly 16 _(i), and the support wheels 50 ₁-50 ₈ aremounted to the frame element 43 ₁ in a bottom region of the trackassembly 16 _(i) between the wheel devices 54 ₁-54 ₄. Each of thesupport wheels 50 ₁-50 ₈ may be directly rotatably mounted to the frameelement 43 ₁ or may be rotatably mounted to a link which is rotatablymounted to the frame element 43 ₁ and to which is rotatably mounted anadjacent one of the support wheels 50 ₁-50 ₈, thus forming a “tandem”.In other embodiments, the frame 44 may be configured in various othermanners.

In this embodiment, the frame 44 is pivotable about a pivot point 51 tofacilitate motion of the track assembly 16 _(i) on uneven terrain andenhance its traction on the ground. More specifically, in this case, thepivot point 51 corresponds to the axle 49 on which the drive wheel 42 ismounted. The frame 44 is pivotally connected at the pivot point 51 bythe frame elements 43 ₂, 43 ₃ that converge towards this point. In thisway, the frame 44, and thus the track assembly 16 _(i), can pivot aboutthe pivot point 51 to deal with uneven terrain the ATV 10 may traverse.In other embodiments, the frame 44 may not be able to pivot about anypivot point.

The support wheels 50 ₁-50 ₈ do not convert power supplied by the primemover 12 to motive force, but rather support and distribute part of theweight of the ATV 10 on the ground as well as guide the track 41 as itis driven by the drive wheel 42. The support wheels 50 ₁-50 ₈ roll onthe inner side 45 of the track 41 along the bottom run of the track 41to apply the bottom run on the ground.

Each of the wheel devices 54 ₁-54 ₄ is a device comprising at least onewheel. In this embodiment, the wheel device 54 ₁ comprises a wheel 77 ₁,the wheel device 54 ₂ comprises a wheel 77 ₂, the wheel device 54 ₃comprises a wheel 77 ₃, and the wheel device 54 ₄ comprises a wheel 77₄. The wheels 77 ₁, 77 ₂ are leading idler wheels, and the wheels 77 ₃,77 ₄ are trailing idler wheels. The wheel devices 54 ₁, 54 ₂ are spacedapart along the widthwise direction of the track assembly 16 _(i), andso are the wheel devices 54 ₃, 54 ₄.

The wheel devices 54 ₁, 54 ₂ are rotatable about respective axes ofrotation 78, 79. In this embodiment, the axes of rotation 78, 79 arealigned with one another to constitute a common axis of rotation 80.More specifically, in this example, the wheel devices 54 ₁, 54 ₂ arerotatably mounted to the frame 44 via an axle 56 which provides the axisof rotation 80. In other examples, the wheel devices 54 ₁, 54 ₂ may bemounted to the frame 44 via respective axles which are aligned with oneanother and which provide the axes of rotation 78, 79. In otherembodiments, the axis of rotation 78 and the axis of rotation 79 may beoffset from one another.

Each of the wheel devices 54 ₁, 54 ₂ contacts the inner side 45 of theendless track 41 such that a longitudinal end segment 50 of the endlesstrack 41 turns around that wheel device. That is, each of the wheeldevices 54 ₁, 54 ₂ contacts both the top run of the endless track 41 andthe bottom run of the endless track 41 such that the longitudinal endsegment 50 of the endless track 41 includes a longitudinal end part ofthe top run of the endless track 41 and a longitudinal end part of thebottom run of the endless track 41. In this embodiment, the longitudinalend segment 50 of the endless track 41 is located between the axis ofrotation 80 of the wheeled devices 54 ₁, 54 ₂ and the longitudinal end57 of the track assembly 16 _(i). In embodiments in which the axis ofrotation 78 and the axis of rotation 79 are offset from one another, thelongitudinal end segment 50 of the endless track 41 is located betweenthe longitudinal end 57 of the track assembly 16, and a given one of theaxes of rotation 78, 79 which is closest to the longitudinal end 57 ofthe track assembly 16 _(i). Thus, in this example, the longitudinal endsegment 50 of the endless track 41 is that segment of the track 41between points A₁ and B₁.

The wheel devices 54 ₁, 54 ₂ are leading wheel devices that maintain thetrack 41 in tension, and can help to support and distribute part of theweight of the ATV 10 on the ground.

In addition, the wheel devices 54 ₁-54 ₄ facilitate use of the ATV 10when the ATV 10 encounters obstacles (e.g., rocks, portions of trees,debris, bumps, abrupt changes in ground level, etc.) on the ground. Forinstance, each of the wheel devices 54 ₁-54 ₄ may absorb shocks when thetrack assembly 16 _(i) encounters obstacles on the ground and/or maymake it easier for the track assembly 16 _(i) to surmount obstacles onthe ground.

Each of the wheel devices 54 ₁, 54 ₂ allows a change in curvature of thelongitudinal end segment 50 of the endless track 41 when thelongitudinal end segment 50 of the endless track 41 contacts an obstacleon the ground. This may absorb a shock resulting from contact with theobstacle and/or may make it easier for the track assembly 16 _(i) tosurmount the obstacle.

More particularly, in this embodiment, the wheels 77 ₁, 77 ₂ areresilient wheels which are elastically deformable. That is, each of theresilient wheels 77 ₁, 77 ₂ can deform under load and regain itsoriginal shape upon removal of the load. When the longitudinal endsegment 50 of the endless track 21 contacts an obstacle on the ground asthe ATV 10 moves, one or both of the resilient wheels 77 ₁, 77 ₂ canelastically deform to allow a change in curvature of the longitudinalend segment 50 of the endless track 21. One or both of the resilientwheels 77 ₁, 77 ₂ can be compressed under load of the ATV 10 to allowthe longitudinal end segment 50 of the endless track 21 to change incurvature in order to generally conform to a contacted part of theobstacle. This elastic deformation of one or both of the resilientwheels 77 ₁, 77 ₂ absorbs at least part of a shock resulting fromcontact with the obstacle. Also, the change in curvature of thelongitudinal end segment 50 of the endless track 21 may enhance itstraction on the obstacle and can thus facilitate climbing of the trackassembly 16 _(i) over the obstacle. As the obstacle is surmounted andstress on one or both of the resilient wheels 77 ₁, 77 ₂ that had beencompressed is reduced, any of the resilient wheels 77 ₁, 77 ₂ that hadbeen compressed can regain its original shape.

Each of the resilient wheels 77 ₁, 77 ₂ may be elastically deformable todifferent radial extents in various embodiments. For example, in someembodiments, a radial extent E corresponding to at least 5%, in somecases at least 10%, in some cases at least 15%, in some cases at least20%, in some cases at least 25%, in some cases at least 30%, in somecases at least 35%, in some cases at least 40% of an outer radius R ofeach of the resilient wheels 77 ₁, 77 ₂ may be elastically deformable.In this case, the radial extent E of each of the resilient wheels 77 ₁,77 ₂ that is elastically deformable corresponds to about 50% of theouter radius R of that wheel. In some embodiments, an entirety of theresilient wheel may be elastically deformable.

The resilient wheels 77 ₁, 77 ₂ may be compressible radially bydifferent degrees in various embodiments. For example, in someembodiments, each of the resilient wheels 77 ₁, 77 ₂ may be compressibleradially in use (i.e., under loads expected to be experienced when thetrack assembly 16 _(i) encounters obstacles on the ground) by at least5%, in some cases by at least 10%, in some cases by at least 15%, insome cases by at least 20%, in some cases by at least 25%, in some casesby at least 30%, in some cases by at least 35%, and in some cases by atleast 40% of its outer radius R. For instance, in an embodiment whereeach of the resilient wheels 77 ₁, 77 ₂ has an outer radius of 130 mm,each of these resilient wheels may be capable of compressing itselfradially by at least 65 mm (i.e., 50%). The actual degree of compressionof a given one of the resilient wheels 77 ₁, 77 ₂ when the trackassembly 16 _(i) encounters an obstacle will depend on the nature of theobstacle (e.g., its shape, material, etc.) and the load exerted on thatwheel by the ATV 10.

In this embodiment, each of the resilient wheels 77 ₁, 77 ₂ comprises ahub 75 and a deformable wheel portion 58 around the hub 75. The hub 75is rigid and rotatable about the axle 56. For example, the hub 75 maycomprise one or more parts made of rigid metal, plastic, and/orcomposite material.

The deformable wheel portion 58 may constitute a tire. For instance, inthis case, the deformable wheel portion 58 constitutes a non-pneumatictire (i.e., an airless tire). More particularly, in this case, thedeformable wheel portion 58 is made of foam such that the resilientwheel 77 _(i) is a foam wheel (i.e., a wheel at least partly made offoam). The foam is elastically deformable such that it can deform underload and regain its original shape when the load is removed. Varioustypes of foam may be used. For example, in some embodiments, the foammay be polymeric foam (e.g., closed-cell polymeric foam). For instance,in some cases, the foam may be polyurethane foam.

The resilient wheels 77 ₁, 77 ₂ may be implemented in various other waysin other embodiments. For example, in some embodiments, each of theresilient wheels 77 ₁, 77 ₂ may comprise elastic material other thanfoam (e.g., rubber or other elastomeric material), which is capable ofdeforming itself under load and then regaining its original shape uponremoval of the load. As another example, in some embodiments, each ofthe resilient wheels 77 ₁, 77 ₂ may comprise a pneumatic tire.

The wheel devices 54 ₃, 54 ₄ are configured in a manner similar to thewheel devices 54 ₁, 54 ₂. Each of the wheel devices 54 ₃, 54 ₄ contactsthe inner side 45 of the endless track 41 such that a longitudinal endsegment 32 of the endless track 41 turns around that wheeled device. Thelongitudinal end segment 32 of the endless track 41 is located betweenan axis of rotation of the wheel devices 54 ₃, 54 ₄ and the longitudinalend 59 of the track assembly 16 _(i). Thus, in this example, thelongitudinal end segment 32 of the endless track 41 is that segment ofthe track 41 between points A₂ and B₂.

Each of the wheel devices 54 ₃, 54 ₄ allows a change in curvature of thelongitudinal end segment 32 of the endless track 41 when thelongitudinal end segment 32 of the endless track 41 contacts an obstacleon the ground. This may absorb a shock resulting from contact with theobstacle and/or may make it easier for the track assembly 16 _(i) tosurmount the obstacle. More particularly, in this embodiment, the wheels77 ₃, 77 ₄ are resilient wheels which are elastically deformable, asdiscussed above in respect of the wheels 77 ₁, 77 ₂.

The track assemblies 14 ₁, 14 ₂ are located in a front part of the ATV10 to provide traction in this front part. Each track assembly 14 _(i)comprises a track 21, a drive wheel 22, a frame 24, a plurality ofsupport wheels 30 ₁-30 ₆, and a plurality of wheel devices 53 ₁-53 ₄.These components of the track assembly 14 _(i) are respectively similarin construction and function to the track 41, the drive wheel 42, theframe 44, the support wheels 50 ₁-50 ₈, and the wheel devices 54 ₁-54 ₄and will therefore not be further discussed.

With reference now to FIG. 9, there will be described an exampleillustrating how the wheel devices 53 ₁-53 ₄, 54 ₁-54 ₄ of the trackassemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂ may absorb shocks resulting fromcontact with obstacles on the ground and/or may make it easier for thetrack assemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂ to surmount such obstacles.

Although obstacles (e.g., rocks, portions of trees, debris, bumps,abrupt changes in ground level, etc.) come in a variety of differentshapes and sizes, they may all conceptually be viewed, from theperspective of the ATV 10, as representing a variation in ground level,namely a variation between a first ground level just prior to theobstacle and a second ground level corresponding to a top part of theobstacle. For example, a large, irregularly shaped rock can be viewed asrepresenting a variation between a first ground level at a base of therock and a second ground level corresponding to the highest point of therock.

Every obstacle can also be viewed as having a steepness that caninfluence a degree to which it can be easily or not easily overcome. Forexample, when viewing an obstacle as a variation between two groundlevels, the steepness of the obstacle can be viewed as corresponding tothe slope of a line following or tangent to the general profile of theobstacle between these two ground levels. This slope, which willhereinafter be referred to as the “general slope” of the obstacle, mayaffect how the wheel devices 54 ₁-54 ₄, 53 ₁-53 ₄ of the trackassemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂ react to the obstacle in question.

FIG. 9 shows an example of the result of an encounter between thelongitudinal end segment 50 of the endless track 41 of the trackassembly 16 _(i)and an obstacle 68 on the ground. In this example, it isassumed that the obstacle 68 lying in the path of the ATV 10 is a rock.It is further assumed that the ATV 10 was in motion along level groundand that the track assemblies 14 ₁, 14 ₂ in the front part of the ATV 10have already cleared the rock 68 which is now lying directly ahead ofthe track assemblies 16 ₁, 16 ₂ in the rear part of the ATV 10.

Up until the track assembly 16 _(i) contacts the rock 68, the wheeldevices 54 ₁, 54 ₂ is in a state as illustrated in FIGS. 1 and 4, namelyas it is when the ATV 10 is travelling along a level ground surface. Inparticular, the resilient wheels 77 ₁, 77 ₂ have a generallynon-deformed circular shape. The track 41 thus has a curvature as shownin FIGS. 1 and 4, where the longitudinal end segment 50 of the track 41has a convexity which generally corresponds to that of a circular arcdefined by the generally non-deformed circular shape of the resilientwheels 77 ₁, 77 ₂.

When the longitudinal end segment 50 of the endless track 41 of thetrack assembly 16 _(i) contacts the rock 68, one or both of the wheeldevices 54 ₁, 54 ₂ react to this contact. More particularly, in thisexample, under load of the ATV 10, the resilient wheels 77 ₁, 77 ₂ arecompressed to allow the longitudinal end segment 50 of the track 41 tochange in curvature in order to generally conform to a part of the rock68 that is engaged by the track 41. Specifically, the compression of theresilient wheels 77 ₁, 77 ₂ induces a change in curvature of thelongitudinal end segment 50 of the track 41. This change in curvature ofthe longitudinal end segment 50 of the track 41 allows it to generallyconform to the general slope of the rock 68. In this case, the change incurvature is such that the portion of the track 41 contacting thecompressed section of the resilient wheels 77 ₁, 77 ₂ is orientedgenerally upwardly and forwardly at an angle corresponding generally tothe general slope of the rock 68. At that point, the longitudinal endsegment 50 of the track 41 is more convex than it was prior to the trackassembly 16 _(i) contacting the rock 68. This elastic deformation of oneor both of the resilient wheels 77 ₁, 77 ₂ absorbs at least part of ashock resulting from contact with the rock 68. Also, the change in shapeof the track 41 thus enhances its traction on the rock 68 and thusfacilitates climbing of the track assembly 16 _(i) over the rock 68.

As the track assembly 16 _(i) reaches the top part of the rock 68 andthen moves down the rock 68, stress on the resilient wheels 77 ₁, 77 ₂is reduced causing each of the resilient wheels 77 ₁, 77 ₂ to regain itsoriginal shape. In turn, this causes the longitudinal end segment 50 ofthe track 41 to regain its original curvature. Upon having cleared therock 68, the track assembly 16 _(i) continues to operate in the state asshown in FIGS. 1 and 4.

It will thus be appreciated that the wheel devices 53 ₁-53 ₄, 54 ₁-54 ₄of the track assemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂ allows the ATV 10 toabsorb shocks resulting from contact with obstacles on the ground and/orallows the ATV 10 to more easily overcome such obstacles. In particular,by allowing a change in curvature of a longitudinal end segment of itsendless track, each of the track assemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂allows that segment of the track \ to generally conform to anencountered obstacle. In other words, each of the track assemblies 14 ₁,14 ₂, 16 ₁, 16 ₂ provides a way to change the shape of a longitudinalend segment of its endless track based on the size and shape of theobstacle encountered. This local elastic deformation of the track mayabsorb the shock resulting from contact with the obstacle. This localelastic deformation may also allow more of its ground-engaging side 47to come into contact with the obstacle, thus providing an increasedsurface area that can allow the track assembly 14 _(i), 16 _(i) to moreeasily climb over the obstacle. This is useful for obstacles of variousshapes and sizes, but especially for those obstacles that wouldotherwise present problems for a traditional idler wheel. For example,once the track assemblies 14 ₁, 14 ₂ have cleared an obstacle such thatthe obstacle is now located between the track assemblies 14 ₁, 14 ₂ andthe track assemblies 16 ₁, 16 ₂, the obstacle surmounting device 54 ₁ ofeach of the track assemblies 16 ₁, 16 ₂ can make it easier for the trackassemblies 16 ₁, 16 ₂ to overcome the obstacle than it would otherwiseif the track assemblies 16 ₁, 16 ₂ had, instead of their respectiveobstacle surmounting device 54 ₁, one or more traditional idler wheelsthat could have certain difficulty in overcoming the obstacle, forinstance, due to a tendency of a front region of that track assembly to“dig” or “wedge” itself at the obstacle's base instead of climbing overthe obstacle.

While in this embodiment the track assemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂ areconfigured in a particular way, they may be configured in various otherways in other embodiments.

For example, in some embodiments, the track assembly 14 _(i), 16 _(i)may comprise more or less than two resilient wheels (such as theresilient wheels 77 ₁-77 ₄) adjacent to each of its longitudinal ends.For instance, in some embodiments, the track assembly 14 _(i), 16 _(i)may comprise a single resilient wheel or three or more resilient wheelsadjacent to each of its longitudinal ends.

As another example, in some embodiments, one or more of the supportwheel 50 ₁-50 ₈ may be resilient wheels that are elastically deformableas discussed above in connection with the resilient wheels 77 ₁-77 ₄.For instance, in some cases, one or more of the support wheel 50 ₁-50 ₈may be resilient wheels similar in construction to, but smaller than,the resilient wheels 77 ₁-77 ₄

As yet another example, instead of having wheel devices 53 _(i), 54 _(i)positioned in respective front and rear longitudinal end regions 89, 99of the track assembly 14 _(i), 16 _(i), in some embodiments, the trackassembly 14 _(i), 16 _(i) may comprise wheel devices 53 _(i), 54 _(i)only in one of its front and rear longitudinal end regions. In suchembodiments, one or more conventional rigid idler wheels may be providedin the longitudinal end region of the track assembly 14 _(i), 16 ₁ wherethere is no wheel device 53 _(i), 54 _(i).

Although in this embodiment each of the track assemblies 14 ₁, 14 ₂, 16₁, 16 ₂ comprises wheel devices 53 _(i), 54 _(i), in other embodiments,some of the track assemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂ may not comprise anysuch wheel device 53 _(i), 54 _(i),.

Turning now to FIGS. 10 and 11, there is shown another embodiment inwhich the ATV 10 comprises track assemblies 14′₁, 14′₂, 16′₁, 16′₂,instead of the track assemblies 14 ₁, 14 ₂, 16 ₁, 16 ₂ discussedpreviously.

The track assemblies 14′₁, 14′₂ are located in a front part of the ATV10 to provide traction in this front part. Each track assembly 14′_(i)comprises a track 21′, a drive wheel 22′, a frame 24′, a pair of frontidler wheels 26 ₁, 26 ₂, a pair of rear idler wheels 28 ₁, 28 ₂, and aplurality of support wheels 30′₁-30′₈ located longitudinally betweenthese front and rear idler wheels.

The track 21′, the drive wheel 22′, the frame 24′ and the support wheels30′₁-30′₈ of the track assembly 14′_(i) are respectively similar inconstruction and function to the track 21, the drive wheel 22, the frame24, and the support wheels 30 ₁-30 ₆ of the track assembly 14 _(i)discussed previously.

The front idler wheels 26 ₁, 26 ₂ are rotatably mounted to the frame 24′in a front longitudinal end region 37′ of the track assembly 14′₁, whilethe rear idler wheels 28 ₁, 28 ₂ are rotatably mounted to the 24′ in arear longitudinal end region 39′ of the track assembly 14′_(i). However,in contrast to the resilient wheels of the wheel devices 53 ₁-53 ₄ ofthe track assembly 14 _(i), the front idler wheels 26 ₁, 26 ₂ and therear idler wheels 28 ₁, 28 ₂ are rigid wheels which do not elasticallydeform under load of the ATV 10 to induce a change in curvature of thetrack 21.

The track assemblies 16′₁, 16′₂ are located in a rear part of the ATV 10to provide traction in this rear part. Each track assembly 16′_(i)comprises a track 41′, a drive wheel 42′, a frame 44′, a pair of rearidler wheels 48 ₁, 48 ₂, a plurality of support wheels 50′₁-50′₁₀, and apair of wheel devices 54′₁, 54′₂.

The track 41′, the drive wheel 42′, the frame 44′ and the support wheels50′₁-50′₈ of the track assembly 16′_(i) are respectively similar inconstruction and function to the track 41, the drive wheel 42, the frame44, and the support wheels 50 ₁-50 ₈ of the track assembly 16 _(i)discussed previously.

The rear idler wheels 48 ₁, 48 ₂ roll on the inner side 45′ of the track41′ such that the longitudinal end segment 32′ of the track 41′ turnsaround these wheels. Like the rear idler wheels 28 ₁, 28 ₂ of the trackassembly 14′₁, the rear idler wheels 48 ₁, 48 ₂ are rigid wheels whichdo not elastically deform under load of the ATV 10 to induce a change incurvature of the track 41′.

Each of the wheel devices 54′₁, 54′₂ is a device comprising at least onewheel. In this embodiment, the wheel device 54′₁ comprises a wheelcarrier 60 and three carried wheels 62 ₁-62 ₃ rotatably mounted to thewheel carrier 60, and the wheel device 54′₂ comprises a wheel carrier 64and three carried wheels 66 ₁-66 ₃ rotatably mounted to the wheelcarrier 64.

The wheel devices 54′₁, 54′₂ are rotatable about respective axes ofrotation 61, 67. In this embodiment, the axes of rotation 61, 67 arealigned with one another to constitute a common axis of rotation 87.More specifically, in this example, the wheel devices 54′₁, 54′₂ arerotatably mounted to the frame 44′ via an axle 34 which provides theaxis of rotation 87. In other examples, the wheel devices 54′₁, 54′₂ maybe mounted to the frame 44′ via respective axles which are aligned withone another and which provide the axes of rotation 61, 67. In otherembodiments, the axis of rotation 61 and the axis of rotation 67 may beoffset from one another.

Each of the wheel devices 54′₁, 54′₂ contacts the inner side 45 of theendless track 41′ such that a longitudinal end segment 50′ of theendless track 41′ turns around that wheel device. That is, each of thewheel devices 54′₁, 54′₂ contacts both the top run of the endless track41′ and the bottom run of the endless track 41′ such that thelongitudinal end segment 50′ of the endless track 41′ includes alongitudinal end part of the top run of the endless track 41′ and alongitudinal end part of the bottom run of the endless track 41′. Inthis embodiment, the longitudinal end segment 50′ of the endless track41′ is located between the axis of rotation 87 of the wheel devices54′₁, 54′₂ and the longitudinal end 57′ of the track assembly 16′_(i).In embodiments in which the axis of rotation 61 and the axis of rotation67 are offset from one another, the longitudinal end segment 50′ of theendless track 41′ is located between the longitudinal end 57′ of thetrack assembly 16′_(i) and a given one of the axes of rotation 61, 67which is closest to the longitudinal end 57′ of the track assembly16′_(i). Thus, in this example, the longitudinal end segment 50′ of theendless track 41′ is that segment of the track 41′ between points A₁′and B₁′.

Each of the wheel devices 54′₁, 54′₂ allows a change in curvature of thelongitudinal end segment 50′ of the endless track 41′ when thelongitudinal end segment 50′ of the endless track 41′ contacts anobstacle on the ground. This may absorb a shock resulting from contactwith the obstacle and/or may make it easier for the track assembly16′_(i) to surmount the obstacle.

With respect to the wheel device 54′₁, the wheel carrier 60 is rotatablymounted to the frame 44′ and adapted to turn about the axis 61. Thecarried wheels 62 ₁-62 ₃ are mounted to the wheel carrier 60 and able torotate about respective axes of rotation. In this embodiment, thecarried wheels 62 ₁-62 ₃ are disposed around the axis 61 (i.e., a closedimaginary line connecting their respective axes of rotation surroundsthe axis 61).

More particularly, in this embodiment, the wheel carrier 60 comprisesthree arms 65 ₁-65 ₃ that extend radially outward from the axis 61. Inthis case, the arms 65 ₁-65 ₃ have the same length and are spaced atequal angles from one another. In other embodiments, the wheel carrier60 may be configured in various other ways. For example, in someembodiments, instead of being a unitary structural element, the wheelcarrier 60 may comprise two or more separate structural elements eachcarrying one or more of the carried wheels 62 ₁-62 ₃ (e.g., three linkseach individually mounted to a common axle forming the axis 61 and eachcarrying one of the carried wheels 62 ₁-62 ₃).

Each of the carried wheels 62 ₁-62 ₃ is mounted to an axle on the wheelcarrier 60 that defines the axis of rotation of that carried wheel.Specifically, in this embodiment, the carried wheel 62 ₁ is rotatablymounted to the arm 65 ₁, the carried wheel 62 ₂ is rotatably mounted tothe arm 65 ₂, and the carried wheel 62 ₃ is rotatably mounted to the arm65 ₃. The carried wheels 62 ₁-62 ₃ are thus arranged in a triangularconfiguration, their respective axes of rotation defining a triangle inwhich is located the axis 61 about which the wheel carrier 60 can turn.

Each of the carried wheels 62 ₁-62 ₃ may rotate about its respectiveaxis of rotation independently of the wheel carrier 60. When the wheelcarrier 60 turns about the axis 61, the carried wheels 62 ₁-62 ₃ (whichare mounted to the member 60) turn about the axis 61 and may also rotateabout their respective axes of rotation.

More specifically, in this embodiment, when the ATV 10 is in motionalong a ground surface that is free of obstacles, the carried wheels 62₁-62 ₃ roll on the inner side 45′ of the track 41′ by rotating abouttheir respective axes of rotation. During this time, the wheel carrier60 and the carried wheels 62 ₁-62 ₃ may be positioned such as shown inFIG. 13, where the carried wheels 62 ₂ and 62 ₃ are generally alignedwith the support wheels 50′₁-50′₅, while the carried wheel 62 ₁ liesabove the support wheels 50′₁-50′₅. Also, in this position, the carriedwheels 62 ₂ and 62 ₃ are positioned such that their respective axes ofrotation lie slightly below the axis 61 while the carried wheel 62 ₁ ispositioned such that its axis of rotation lies above the axis 61. As aresult, the wheel carrier 60 and the carried wheels 62 ₁-62 ₃ impart agiven curvature to the longitudinal end segment 50′ of the endless track41′. This given curvature is such that the longitudinal end segment 50′of the endless track 41′ has a certain convexity, which in this case isuseful for travelling along a level ground surface as it maximizes thecontact area between the track 41′ and the level ground surface.

When the longitudinal end segment 50′ of the endless track 41′ comesinto contact with an obstacle on the ground, the wheel carrier 60 turnsabout the axis 61 to allow the track assembly 16′_(i) to overcome theobstacle. Specifically, because the carried wheels 62 ₁-62 ₃ arerotatably mounted to the wheel carrier 60, they also turn about the axis61 when the wheel carrier 60 turns. As the carried wheels 62 ₁-62 ₃ rollon the inner side 45′ of the track 41′, this turning motion of the wheelcarrier 60 and the carried wheels 62 ₁-62 ₃ about the axis 61 induces achange in curvature of the longitudinal end segment 50′ of the endlesstrack 41′. This motion of the wheel carrier 60 and the carried wheels 62₁-62 ₃ can absorb at least part of a shock resulting from contact withthe obstacle. Also, the change in curvature of the longitudinal endsegment 50′ of the endless track 41′ allows that segment of the track41′ to generally conform to the obstacle being encountered and canfacilitate its surmounting.

While it can rotate about the axis of rotation 61, the wheel device 54′₁may be configured such that, in use, it does not necessarily make acomplete rotation (i.e., a 360° rotation) about the axis 61. This is incontrast to the wheel devices 54 ₁-54 ₄, 53 ₁-53 ₄ discussed previouslywhich, in use, make complete rotations about their respective axes ofrotation.

The wheel device 54′₂ is spaced apart from the wheel device 54′₁ alongthe widthwise direction of the track assembly 16 _(i). The wheel carrier64 is rotatably mounted to the frame 44′ and adapted to turn about theaxis 67. The carried wheels 66 ₁-66 ₃ are mounted to the wheel carrier64 and able to rotate about respective axes of rotation. In thisembodiment, the carried wheels 66 ₁-66 ₃ are disposed around the axis 67(i.e., an imaginary closed line connecting their respective axes ofrotation surrounds the axis 67).

More particularly, in this embodiment, analogously to the wheel carrier60 and the carried wheels 62 ₁-62 ₃, the wheel carrier 64 comprisesthree arms 69 ₁-69 ₃ that extend radially outward from the axis 67, withthe carried wheels 66 ₁-66 ₃ being rotatably mounted to respective onesof the arm 69 ₁-69 ₃. Thus, each of the carried wheels 66 ₁-66 ₃ mayrotate about its respective axis of rotation independently of the wheelcarrier 64, and, when the wheel carrier 64 turns about the axis 67, thecarried wheels 66 ₁-66 ₃ turn about the axis 67 and may also rotateabout their respective axes of rotation.

With reference now to FIGS. 20 and 21, there will be described examplesillustrating how the wheel devices 54′₁, 54′₂ of the track assembly16′_(i) operate when the ATV 10 encounters obstacles on the ground.

As will be discussed, in this embodiment, the general slope of anencountered obstacle affects how the wheel devices 54′₁, 54′₂ of thetrack assembly 16′_(i) may react to the obstacle. In particular, whenthe general slope of the obstacle is not at a relatively steep angle,the wheel devices 54′₁, 54′₂ may react in a first manner by turningabout their axes 61, 67 in a clockwise direction. For example, if thewheel devices 54′₁, 54′₂ encounter a relatively small bump on theground, they may react in this first manner. In contrast, when thegeneral slope of the obstacle is relatively steep, wheel devices 54′₁,54′₂ may react in a second, different manner by turning about their axes61, 67 in a counterclockwise direction. For example, if the ATV 10 isrequired to overcome a relatively large, irregularly shaped rock, thewheel devices 54′₁, 54′₂ may react in this second manner.

FIG. 20 shows an example of the result of an encounter between the wheeldevices 54′₁, 54′₂ of the track assembly 16′_(i) and an obstacle 71having a relatively small size. In this example, it is assumed that theobstacle 71 lying in the path of the ATV 10 is a portion of the trunk ofa relatively small tree having fallen on the ground. It is furtherassumed that the ATV 10 was in motion along level ground and that thetrack assemblies 14′₁, 14′₂ in the front part of the ATV 10 have alreadycleared the trunk portion 71 which is now lying directly ahead of thetrack assemblies 16′₁, 16′₂ in the rear part of the ATV 10.

Up until the track assembly 16′_(i) contacts the trunk portion 71, thevarious components of the wheel devices 54′₁, 54′₂ are positioned asillustrated in FIGS. 10 and 13, namely as they are when the ATV 10 istravelling along a level ground surface. More specifically, the wheelcarriers 60, 64 are in an angular position where: each of the carriedwheels 62 ₁, 66 ₁ lies above the axis 61, 67; each of the carried wheels62 ₂, 66 ₂, 62 ₃, 66 ₃ is in a vertical position that is generally belowthe carried wheels 62 ₁, 66 ₁; and the carried wheels 62 ₃, 66 ₃ arelocated longitudinally in front of the carried wheels 62 ₂, 66 ₂.

When the longitudinal end segment 50′ of the endless track 41′ contactsthe trunk portion 71 at a contact point, the wheel devices 54′₁, 54′₂react to this contact. In this example, the general slope of the trunkportion 71 may be seen as being relatively shallow. The general slope ofthe trunk portion 71 determines where the contact point between thetrunk portion 71 and the track 41′ may occur, which determines themanner in which the wheel devices 54′₁, 54′₂ react to the trunk portion71. In this case, the gentle angle of the general slope causes the track41′ to contact the trunk portion 71 at a location on the track 41′ thatis generally longitudinally aligned with a lower portion of each of thecarried wheels 62 ₃, 66 ₃ (i.e., a portion below its respective axis ofrotation). As a result, the carried wheels 62 ₃, 66 ₃ are forced upwardsand, as they are mounted to the wheel carriers 60, 64, they cause thewheel carriers 60, 64 to turn about the axis 61, 67 in a clockwisedirection.

This turning motion of the wheel carriers 60, 64 in a clockwisedirection adjusts the angular position of each of the carried wheels 62₁, 66 ₁, 62 ₂, 66 ₂. Specifically, in this case, this turning motioncauses each of the carried wheels 62 ₁, 66 ₁ to follow an arc to a newangular position that may be vertically lower than and rearward of itsoriginal position, while it causes each of the carried wheels 62 ₂, 66 ₂to move slightly lower and forwardly of its original position.

The wheel carriers 60, 64 and the carried wheels 62 ₁-62 ₃, 66 ₁-66 ₃turning about the axis 61, 67 induces a change in curvature of thelongitudinal end segment 50′ of the endless track 41′. In particular,the change in curvature of the longitudinal end segment 50′ of theendless track 41′ allows that segment of the track 41′ to generallyconform to the general slope of the trunk portion 71 and can facilitateits surmounting. Indeed, in this example, the change in curvature issuch that the portion of the track 41′ between the carried wheels 62 ₃,66 ₃ and the carried wheels 62 ₂, 66 ₂ is oriented generally upwardlyand forwardly at an angle corresponding generally to the general slopeof the trunk portion 71.

In this example, upon reaching the top part of the trunk portion 71, thewheel devices 54′₁, 54′₂ proceed to go down the trunk portion 71 andreturn to the first ground level. In this case, the wheel devices 54′₁,54′₂ operate in a manner reverse to that previously described. Inparticular, as the carried wheels 62 ₃, 66 ₃ follow a general downwardslope of the trunk portion 71 to return to the first ground level, theyare forced downwards and thus cause the wheel carriers 60, 64 to turnabout the axis 61, 67 in a counterclockwise direction. This turningmotion of the wheel carriers 60, 64 in a counterclockwise directionadjusts the angular position of each of the carried wheels 62 ₁, 66 ₁,62 ₂, 66 ₂.

Once the wheel devices 54′₁, 54′₂ have cleared the trunk portion 71, thewheel carriers 60, 64 and the carried wheels 62 ₁-62 ₃, 66 ₁-66 ₃ returnto their original positions as shown in FIGS. 10 and 13.

FIG. 21 shows an example of the result of an encounter between the wheeldevices 54′₁, 54′₂ of the track assembly 16′_(i) and an obstacle 73having a relatively large size. In this example, it is assumed that theobstacle 73 lying in the path of the ATV 10 is a rock having arelatively large size. It is further assumed that the ATV 10 was inmotion along level ground and that the track assemblies 14′₁, 14′₂ inthe front part of the ATV 10 have already cleared the rock 73 which isnow lying directly ahead of the track assemblies 16′₁, 16′₂ in the rearpart of the ATV 10.

Up until the track assembly 16′_(i) contacts the rock 73, the variouscomponents of the wheel devices 54′₁, 54′₂ are positioned as illustratedin FIGS. 10 and 13, namely as they are when the ATV 10 is travellingalong a level ground surface. More specifically, the wheel carriers 60,64 are in an angular position where: each of the carried wheels 62 ₁, 66₁ lies above the axis 61, 67; each of the carried wheels 62 ₂, 66 ₂, 62₃, 66 ₃ is in a vertical position that is generally below the carriedwheels 62 ₁, 66 ₁; and the carried wheels 62 ₃, 66 ₃ are locatedlongitudinally in front of the carried wheels 62 ₂, 66 ₂.

When the longitudinal end segment 50′ of the endless track 41′ contactsthe rock 73 at a contact point, the wheel devices 54′₁, 54′₂ react tothis contact. In this example, the general slope of the rock 73 has arelatively steep angle. The general slope of the rock 73 determineswhere the contact point between the rock 73 and the track 41′ may occur,which determines the manner in which the wheel devices 54′₁, 54′₂ reactto the rock 73. In this case, the steep angle of the general slopecauses the track 41′ to contact the rock 73 at a location on the track41′ that is generally longitudinally aligned with a mid-portion of eachof the carried wheels 62 ₃, 66 ₃ (i.e., a portion vertically alignedwith its respective axis of rotation). The position of this contactpoint causes the carried wheels 62 ₃, 66 ₃ to momentarily stop moving.Because of the forward momentum of the track assembly 16′_(i), thecarried wheels 62 ₃, 66 ₃ act as a temporary pivot and, as they aremounted to the wheel carriers 60, 64, they cause the wheel carriers 60,64 to turn about the axis 61, 67 in a counterclockwise direction.

This turning motion of the wheel carriers 60, 64 in a counterclockwisedirection adjusts the angular position of each of the carried wheels 62₁, 66 ₁, 62 ₂, 66 ₂. Specifically, in this case, this turning motioncauses each of the carried wheels 62 ₁, 66 ₁ to follow an arc to a newangular position where it also engages the rock 73 via the track 41,while it causes each of the carried wheels 62 ₂, 66 ₂ to move upwardly.

The wheel carriers 60, 64 and the carried wheels 62 ₁-62 ₃, 66 ₁-66 ₃turning about the axis 61, 67 induces a change in curvature of thelongitudinal end segment 50′ of the endless track 41′. In particular,the change in curvature of the longitudinal end segment 50′ of theendless track 41′ allows that segment of the track 41′ to generallyconform to the general slope of the rock 73 and can facilitate itssurmounting. Indeed, in this example, the change in curvature is suchthat the portion of the track 41′ between the carried wheels 62 ₃, 66 ₃and the carried wheels 62 ₁, 66 ₁ is oriented generally upwardly at anangle corresponding generally to the general slope of the rock 73. Inthis case, this results in the carried wheels 62 ₁, 66 ₁ and 62 ₃, 66 ₃becoming vertically in-line with each other, since the rock 73 presentsa near-vertical face to the track assembly 16′_(i).

In this example, upon reaching a top part of the rock 73, a secondcounterclockwise rotation of the wheel carriers 60, 64 is initiated.More particularly, up to the point where wheel devices 54′₁, 54′₂ reachthe top part of the rock 73, the carried wheels 62 ₁, 66 ₁ and thecarried wheels 62 ₃, 66 ₃ remain generally vertically in-line with eachother. In this configuration, the carried wheels 62 ₁, 66 ₁ first reachthe top part of the rock 73, which is considerably less steep than thegeneral slope of the rock 73 initially encountered. This change in sloperesults in the contact point between each of the carried wheels 62 ₁, 66₁ and the top part of the rock 73 shifting back towards the lower partof that wheel.

Thus, with the forward momentum of the track assembly 16′_(i), when thecarried wheels 62 ₁, 66 ₁ reach the top part of the rock 73, they causethe wheel carriers 60, 64 to turn about the axis 61, 67 a second time ina counterclockwise direction.

As it goes down the rock 73, the wheel devices 54′₁, 54′₂ operate in amanner reverse to that previously described. In particular, the carriedwheels 62 ₁, 66 ₁ and the carried wheels 62 ₃, 66 ₃ follow a generaldownward slope of the rock 73 to return to the first ground level.

While in this embodiment the wheel devices 54′₁, 54′₂ of each of thetrack assemblies 16′₁, 16′₂ are configured in a particular way, they maybe configured in various other ways in other embodiments.

For example, in some embodiments, two or more than three carried wheels(similar to the carried wheels 62 ₁-62 ₃, 66 ₁-66 ₃) may be rotatablymounted to each of the wheel carriers 60, 64 of the track assembly16′_(i). For instance, in some embodiments, fourcarried wheels may berotatably mounted to any one of the wheel carriers 60, 64. These fourcarried wheels may be arranged in a rectangular configuration, i.e.,their respective axes of rotation may define a rectangle (e.g., asquare) in which is located the axis 61, 67 of the wheel carrier 60, 64to which they are rotatably mounted.

As another example, instead of being all mounted on one lateral side ofeach of the wheel carriers 60, 64, in some embodiments, carried wheelssuch as the carried wheels 62 ₁-62 ₃, 66 ₁-66 ₃ may be mounted on bothlateral sides of any one of the wheel carriers 60, 64. For instance, insome embodiments, two of the carried wheels 66 ₁-66 ₃ may be mounted onthe inner lateral side of the wheel carrier 64 that lies proximate to amain body of the ATV 10, while the remaining one of the carried wheels66 ₁-66 ₃ may be mounted on the opposite, outer lateral side of thewheel carrier 64.

As yet another example, in some embodiments, the track assembly 16 _(i)may comprise more or less than two wheel devices such as the wheeldevices 54′₁, 54′₂. For instance, in some embodiments, the trackassembly 16 _(i) may comprise three or four wheel devices such as thewheel devices 54′₁, 54′₂ that are laterally spaced from one another andeach carry three or more carried wheels such as the carried wheels 62₁-62 ₃, 66 ₁-66 ₃.

As yet another example, instead of being positioned in the frontlongitudinal end region 37′ of the track assembly 16′_(i) in front ofthe support wheels 50′_(i)-50′₁₀, in some embodiments, the wheel devices54′₁, 54′₂ may be positioned in the rear longitudinal end region 39′ ofthe track assembly 16′_(i) behind the support wheels 50′₁-50′₁₀ toreplace the rear idler wheels 48 ₁, 48 ₂. Alternatively, in otherembodiments, the track assembly 16′_(i) may comprise wheel devices suchas the wheel devices 54′₁, 54′₂ both in the front longitudinal endregion 37′ of the track assembly 16′_(i) and in the rear longitudinalend region 39′ of the track assembly 16′_(i).

Although in this embodiment each of the track assemblies 16′₁, 16′₂comprises the wheel devices 54′₁, 54′₂ but each of the track assemblies14′₁, 14′₂ does not comprise such wheel devices, in other embodiments,each of the track assemblies 14′₁, 14′₂ may comprise wheel devices suchas the wheel devices 54′₁, 54′₂ instead of its front idler wheels 26 ₁,26 ₂ and/or its rear idler wheels 28 ₁, 28 ₂.

While in this embodiment the wheel devices 53 ₁-53 ₄, 54 ₁-54 ₄, 54′₁,54′₂ are used as part of track assemblies of an ATV, in otherembodiments, similar wheel devices constructed according to principlesdiscussed herein may be used as part of track assemblies of other typesof tracked vehicles. For example, in some embodiments, a wheel deviceconstructed according to principles discussed herein may be used as partof a track assembly of a snowmobile. As another example, in someembodiments, a wheel device constructed according to principlesdiscussed herein may be used as part of a track assembly of a workvehicle, such as a construction vehicle (e.g., a bulldozes, a backhoeloader, an excavator, etc.), an agricultural vehicle (e.g., a harvester,a combine, a tractor, etc.) a forestry vehicle (e.g., a feller-buncher,a tree chipper, a knuckleboom loader, etc.) or any other vehicleoperable off-road.

Although various embodiments and examples have been presented, this wasfor the purpose of describing, but not limiting, the invention. Variousmodifications and enhancements will become apparent to those of ordinaryskill in the art and are within the scope of the invention, which isdefined by the appended claims.

1-47. (canceled)
 48. A track assembly for traction of a vehicle, thetrack assembly comprising: a) a track comprising a ground-engaging outerside for engaging the ground and an inner side opposite to theground-engaging outer side; and b) a track-engaging arrangement fordriving and guiding the track around the track-engaging arrangement, abottom run of the track extending under the track-engaging arrangement,the track-engaging arrangement comprising: i. a frame; ii. a drive wheelfor driving the track; iii. an idler wheel adjacent to a longitudinalend of the track assembly and contacting the bottom run of the track;and iv. a wheel-carrying structure carrying the idler wheel and turnablerelative to the frame about an axis to change a shape of the track, theidler wheel being rotatable relative to the wheel-carrying structure, anaxis of rotation of the idler wheel being different from the axis aboutwhich the wheel-carrying structure is turnable.
 49. The track assemblyof claim 48, wherein the axis of rotation of the idler wheel is raisedwhen the wheel-carrying structure turns relative to the frame in a firstdirection and lowered when the wheel-carrying structure turns relativeto the frame in a second direction opposite to the first direction. 50.The track assembly of claim 48, wherein the wheel-carrying structure isturnable relative to the frame such that the axis of rotation of theidler wheel is movable from a first position above the axis about whichthe wheel-carrying structure is turnable to a second position below theaxis about which the wheel-carrying structure is turnable
 51. The trackassembly of claim 48, wherein: the idler wheel is a front idler wheel;the longitudinal end of the track assembly is a front longitudinal endof the track assembly; and the track-engaging arrangement comprises arear idler wheel adjacent to a rear longitudinal end of the trackassembly and contacting the bottom run of the track.
 52. The trackassembly of claim 51, wherein the frame comprises an elongated memberextending from the wheel-carrying structure to the rear idler wheel. 53.The track assembly of claim 52, wherein the elongated member isconfigured to diverge from the ground towards the wheel-carryingstructure.
 54. The track assembly of claim 53, wherein the elongatedmember is configured to diverge from the ground towards the rear idlerwheel.
 55. The track assembly of claim 51, wherein: the track-engagingarrangement comprises a plurality of support wheels disposed between thefront idler wheel and the rear idler wheel in a longitudinal directionof the track assembly and contacting the bottom run of the track; andthe axis about which the wheel-carrying structure is turnable is higherthan an axis of rotation of a given one of the support wheels.
 56. Thetrack assembly of claim 48, wherein the axis about which thewheel-carrying structure is turnable and the axis of rotation of theidler wheel are parallel.
 57. The track assembly of claim 48, whereinthe frame is mounted about an axis of rotation of the drive wheel. 58.The track assembly of claim 51, wherein the frame has a pivot pointlocated between the front idler wheel and the rear idler wheel in alongitudinal direction of the track assembly.
 59. The track assembly ofclaim 58, wherein the pivot point of the frame corresponds to an axis ofrotation of the drive wheel.
 60. The track assembly of claim 51, whereinthe axis of rotation of the front idler wheel and an axis of rotation ofthe rear idler wheel are movable relative to an axis of rotation of thedrive wheel when the track assembly moves on the ground.
 61. The trackassembly of claim 51, wherein a distance between an axis of rotation ofthe drive wheel and the axis of rotation of the front idler wheel in alongitudinal direction of the track assembly is different from adistance between the axis of rotation of the drive wheel and an axis ofrotation of the rear idler wheel in the longitudinal direction of thetrack assembly.
 62. The track assembly of claim 48, wherein a distancebetween the axis of rotation of the idler wheel and the axis about whichthe wheel-carrying structure is turnable is greater than a radius of theidler wheel.
 63. The track assembly of claim 51, wherein: thetrack-engaging arrangement comprises a plurality of support wheelsdisposed between the front idler wheel and the rear idler wheel in alongitudinal direction of the track assembly; and a distance between theaxis of rotation of the front idler wheel and the axis about which thewheel-carrying structure is turnable is less than a distance between theaxis about which the wheel-carrying structure is turnable and an axis ofrotation of a given one of the support wheels that is closest to thewheel-carrying structure.
 64. The track assembly of claim 48, wherein:the idler wheel is a first idler wheel; the track-engaging arrangementcomprises a second idler wheel spaced apart from the first idler wheelin a widthwise direction of the track assembly; the wheel-carryingstructure carries the second idler wheel; the second idler wheel isrotatable relative to the wheel-carrying structure; and an axis ofrotation of the second idler wheel is different from the axis aboutwhich the wheel-carrying structure is turnable.
 65. The track assemblyof claim 48, wherein the inner side of the track comprises a pluralityof wheel-contacting projections for contacting at least one of the drivewheel and the idler wheel.
 66. The track assembly of claim 65, whereinthe wheel-contacting projections are drive projections and the drivewheel comprises a sprocket for engaging the drive projections.
 67. Thetrack assembly of claim 48, wherein the wheel-carrying structurecomprises an arm carrying the idler wheel and extending away from theaxis about which the wheel-carrying structure is turnable.
 68. The trackassembly of claim 48, wherein the idler wheel is one of a plurality ofidler wheels carried by the wheel-carrying structure.
 69. The trackassembly of claim 68, wherein the plurality of idler wheels comprises atleast three idler wheels disposed around the axis about which thewheel-carrying structure is turnable.
 70. The track assembly of claim68, wherein the wheel-carrying structure comprises a plurality of armscarrying respective ones of the idler wheels and extending away from theaxis about which the wheel-carrying structure is turnable.
 71. The trackassembly of claim 48, wherein the wheel-carrying structure is configuredto turn relative to the frame in response to the track assemblycontacting an obstacle on the ground.
 72. The track assembly of claim71, wherein the wheel-carrying structure is configured to turn relativeto the frame in a first direction if the obstacle has a first size andturn relative to the frame in a second direction opposite to the firstdirection if the obstacle has a second size different from the firstsize.
 73. The track assembly of claim 48, wherein the wheel-carryingstructure is turnable relative to the frame such that the axis ofrotation of the idler wheel is movable relative to the frame to changean orientation of a segment of the bottom run of the track extendingfrom the idler wheel to an adjacent part of the track-engagingarrangement in contact with the bottom run of the track relative to theframe.
 74. The track assembly of claim 73, wherein: the track-engagingarrangement comprises a plurality of guiding wheels contacting thebottom run of the track; the idler wheel is one of the plurality ofguiding wheels; and the adjacent part of the track-engaging arrangementin contact with the bottom run of the track is an adjacent one of theguiding wheels.
 75. The track assembly of claim 73, wherein theorientation of the segment of the bottom run of the track extending fromthe idler wheel to the adjacent part of the track-engaging arrangementin contact with the bottom run of the track relative to the framedefines a first angle relative to a longitudinal direction of the trackassembly when the axis of rotation of the idler wheel is in a firstposition relative to the frame and defines a second angle relative tothe longitudinal direction of the track assembly when the axis ofrotation of the idler wheel is in a second position relative to theframe, the second angle being substantially different from the firstangle.
 76. The track assembly of claim 48, wherein the wheel-carryingstructure is turnable relative to the frame such that the axis ofrotation of the idler wheel is movable relative to the frame to createan inflexion point in the bottom run of the track.
 77. The trackassembly of claim 48, wherein the track assembly is steerable byoperating a steering device of the vehicle to change an orientation ofthe track assembly relative to the vehicle.
 78. An all-terrain vehicle(ATV) comprising a set of four track assemblies, wherein each of atleast two of the four track assemblies is as claimed in claim
 48. 79. Atrack assembly for traction of a vehicle, the track assembly comprising:a) a track comprising a ground-engaging outer side for engaging theground and an inner side opposite to the ground-engaging outer side; andb) a track-engaging arrangement for driving and guiding the track aroundthe track-engaging arrangement, a bottom run of the track extendingunder the track-engaging arrangement, the track-engaging arrangementcomprising: i. a frame; ii. a drive wheel for driving the track; andiii. an idler wheel adjacent to a longitudinal end of the track assemblyand contacting the bottom run of the track, an axis of rotation of theidler wheel being movable relative to the frame to change a shape of thetrack.
 80. The track assembly of claim 79, wherein the axis of rotationof the idler wheel is movable relative to the frame to change anorientation of a segment of the bottom run of the track extending fromthe idler wheel to an adjacent part of the track-engaging arrangement incontact with the bottom run of the track relative to the frame.
 81. Thetrack assembly of claim 80, wherein: the track-engaging arrangementcomprises a plurality of guiding wheels contacting the bottom run of thetrack; the idler wheel is one of the plurality of guiding wheels; andthe adjacent part of the track-engaging arrangement in contact with thebottom run of the track is an adjacent one of the guiding wheels. 82.The track assembly of claim 79, wherein the orientation of the segmentof the bottom run of the track extending from the idler wheel to theadjacent part of the track-engaging arrangement in contact with thebottom run of the track relative to the frame defines a first anglerelative to a longitudinal direction of the track assembly when the axisof rotation of the idler wheel is in a first position relative to theframe and defines a second angle relative to the longitudinal directionof the track assembly when the axis of rotation of the idler wheel is ina second position relative to the frame, the second angle beingsubstantially different from the first angle.
 83. The track assembly ofclaim 79, wherein the axis of rotation of the idler wheel is movablerelative to the frame to create an inflexion point in the bottom run ofthe track.
 84. The track assembly of claim 79, wherein: thetrack-engaging arrangement comprises a wheel-carrying structure carryingthe idler wheel and turnable relative to the frame about an axis to movethe axis of rotation of the idler wheel in order to change the shape ofthe track; the idler wheel is rotatable relative to the wheel-carryingstructure; and the axis of rotation of the idler wheel is different fromthe axis about which the wheel-carrying structure is turnable.
 85. Thetrack assembly of claim 84, wherein the axis of rotation of the idlerwheel is raised when the wheel-carrying structure turns relative to theframe in a first direction and lowered when the wheel-carrying structureturns relative to the frame in a second direction opposite to the firstdirection.
 86. The track assembly of claim 84, wherein thewheel-carrying structure is turnable relative to the frame such that theaxis of rotation of the idler wheel is movable from a first positionabove the axis about which the wheel-carrying structure is turnable to asecond position below the axis about which the wheel-carrying structureis turnable
 87. The track assembly of claim 79, wherein: the idler wheelis a front idler wheel; the longitudinal end of the track assembly is afront longitudinal end of the track assembly; and the track-engagingarrangement comprises a rear idler wheel adjacent to a rear longitudinalend of the track assembly and contacting the bottom run of the track.88. The track assembly of claim 87, wherein the frame comprises anelongated member extending between the front idler wheel and the rearidler wheel.
 89. The track assembly of claim 88, wherein the elongatedmember is configured to diverge from the ground towards the front idlerwheel.
 90. The track assembly of claim 89, wherein the elongated memberis configured to diverge from the ground towards the rear idler wheel.91. The track assembly of claim 84, wherein: the idler wheel is a frontidler wheel; the longitudinal end of the track assembly is a frontlongitudinal end of the track assembly; the track-engaging arrangementcomprises a rear idler wheel adjacent to a rear longitudinal end of thetrack assembly and contacting the bottom run of the track, and aplurality of support wheels disposed between the front idler wheel andthe rear idler wheel in a longitudinal direction of the track assemblyand contacting the bottom run of the track; and the axis about which thewheel-carrying structure is turnable is higher than an axis of rotationof a given one of the support wheels.
 92. The track assembly of claim79, wherein the frame is mounted about an axis of rotation of the drivewheel.
 93. The track assembly of claim 87, wherein the frame has a pivotpoint located between the front idler wheel and the rear idler wheel ina longitudinal direction of the track assembly.
 94. The track assemblyof claim 93, wherein the pivot point of the frame corresponds to an axisof rotation of the drive wheel.
 95. The track assembly of claim 79,wherein the axis of rotation of the idler wheel is movable relative toan axis of rotation of the drive wheel when the track assembly moves onthe ground.
 96. The track assembly of claim 87, wherein a distancebetween an axis of rotation of the drive wheel and the axis of rotationof the front idler wheel in a longitudinal direction of the trackassembly is different from a distance between the axis of rotation ofthe drive wheel and an axis of rotation of the rear idler wheel in thelongitudinal direction of the track assembly.
 97. The track assembly ofclaim 84, wherein a distance between the axis of rotation of the idlerwheel and the axis about which the wheel-carrying structure is turnableis greater than a radius of the idler wheel.
 98. The track assembly ofclaim 79, wherein: the idler wheel is a first idler wheel; thetrack-engaging arrangement comprises a second idler wheel spaced apartfrom the first idler wheel in a widthwise direction of the trackassembly; and an axis of rotation of the second idler wheel is movablerelative to the frame to change the shape of the track.
 99. The trackassembly of claim 79, wherein the inner side of the track comprises aplurality of wheel-contacting projections for contacting at least one ofthe drive wheel and the idler wheel.
 100. The track assembly of claim99, wherein the wheel-contacting projections are drive projections andthe drive wheel comprises a sprocket for engaging the drive projections.101. The track assembly of claim 84, wherein the wheel-carryingstructure comprises an arm carrying the idler wheel and extending awayfrom the axis about which the wheel-carrying structure is turnable. 102.The track assembly of claim 84, wherein the idler wheel is one of aplurality of idler wheels carried by the wheel-carrying structure. 103.The track assembly of claim 102, wherein the plurality of idler wheelscomprises at least three idler wheels disposed around the axis aboutwhich the wheel-carrying structure is turnable.
 104. The track assemblyof claim 102, wherein the wheel-carrying structure comprises a pluralityof arms carrying respective ones of the idler wheels and extending awayfrom the axis about which the wheel-carrying structure is turnable. 105.The track assembly of claim 79, wherein the axis of rotation of theidler wheel is movable relative to the frame in response to the trackassembly contacting an obstacle on the ground.
 106. The track assemblyof claim 105, wherein the axis of rotation of the idler wheel is movablerelative to the frame in a first direction if the obstacle has a firstsize and movable relative to the frame in a second direction opposite tothe first direction if the obstacle has a second size different from thefirst size.
 107. The track assembly of claim 79, wherein the trackassembly is steerable by operating a steering device of the vehicle tochange an orientation of the track assembly relative to the vehicle.108. An all-terrain vehicle (ATV) comprising a set of four trackassemblies, wherein each of at least two of the four track assemblies isas claimed in claim
 79. 109. A track assembly for traction of a vehicle,the track assembly comprising: a) a track comprising a ground-engagingouter side for engaging the ground and an inner side opposite to theground-engaging outer side; and b) a track-engaging arrangement fordriving and guiding the track around the track-engaging arrangement, abottom run of the track extending under the track-engaging arrangement,the track-engaging arrangement comprising: i. a frame; ii. a drive wheelfor driving the track; and iii. a plurality of guiding wheels contactingthe bottom run of the track, the plurality of guiding wheels includingan idler wheel adjacent to a longitudinal end of the track assembly, anaxis of rotation of the idler wheel being movable relative to the frameto change an orientation of a segment of the bottom run of the trackextending from the idler wheel to an adjacent one of the guiding wheelsrelative to the frame.
 110. The track assembly of claim 109, wherein theorientation of the segment of the bottom run of the track extending fromthe idler wheel to the adjacent one of the guiding wheels relative tothe frame defines a first angle relative to a longitudinal direction ofthe track assembly when the axis of rotation of the idler wheel is in afirst position relative to the frame and defines a second angle relativeto the longitudinal direction of the track assembly when the axis ofrotation of the idler wheel is in a second position relative to theframe, the second angle being substantially different from the firstangle.
 111. The track assembly of claim 109, wherein the axis ofrotation of the idler wheel is movable relative to the frame to createan inflexion point in the bottom run of the track beneath the adjacentone of the guiding wheels.
 112. The track assembly of claim 109,wherein: the track-engaging arrangement comprises a wheel-carryingstructure carrying the idler wheel and turnable relative to the frameabout an axis to move the axis of rotation of the idler wheel in orderto change the orientation of the segment of the bottom run of the trackextending from the idler wheel to the adjacent one of the guiding wheelsrelative to the frame; the idler wheel is rotatable relative to thewheel-carrying structure; and the axis of rotation of the idler wheel isdifferent from the axis about which the wheel-carrying structure isturnable.
 113. The track assembly of claim 112, wherein thewheel-carrying structure is turnable relative to the frame such that theaxis of rotation of the idler wheel is movable from a first positionabove the axis about which the wheel-carrying structure is turnable to asecond position below the axis about which the wheel-carrying structureis turnable
 114. The track assembly of claim 109, wherein: the idlerwheel is a front idler wheel; the longitudinal end of the track assemblyis a front longitudinal end of the track assembly; and the plurality ofguiding wheels includes a rear idler wheel adjacent to a rearlongitudinal end of the track assembly.
 115. The track assembly of claim114, wherein: the plurality of guiding wheels includes a plurality ofsupport wheels disposed between the front idler wheel and the rear idlerwheel in a longitudinal direction of the track assembly.
 116. The trackassembly of claim 114, wherein the frame has a pivot point locatedbetween the front idler wheel and the rear idler wheel in a longitudinaldirection of the track assembly.
 117. The track assembly of claim 109,wherein the axis of rotation of the idler wheel is movable relative toan axis of rotation of the drive wheel when the track assembly moves onthe ground.
 118. The track assembly of claim 109, wherein the axis ofrotation of the idler wheel is movable relative to the frame in responseto the track assembly contacting an obstacle on the ground.
 119. Thetrack assembly of claim 109, wherein the track assembly is steerable byoperating a steering device of the vehicle to change an orientation ofthe track assembly relative to the vehicle.
 120. An all-terrain vehicle(ATV) comprising a set of four track assemblies, wherein each of atleast two of the four track assemblies is as claimed in claim 109.